Impedance and Gain Problem

Thread Starter


Joined Aug 13, 2007
Hi people. I'm having difficulty finding the forumulae to work out this problem which is part of a large c programming project due next week. Not knowing how this problem works is hindering my progress a lot... Any solutions/insight would be a MASSIVE help. Thanks.

Here's the problem:
A system is made up of a number of Elements (picture below represents a single element) that are modelled as 2-port networks. They are connected in series. Each element is characterised by three values; input impedance (Zi), output impedance (Zo) and gain in dB (GVi).

I need to know the formula or theory behind calculating the overall system's input impedance, output impedance, and end-to-end gain taking into account all gains and coupling losses. (What the hell are coupling losses!?)

Please help!!!???


Joined Aug 4, 2007
If the systems are represented as shown i.e. simply input impedance, output impedance and an ideal amplifier of gain G then the only coupling losses are the power losses within the input and output impedances.

If the ideal amplifier outputs a certain voltage not all that voltage will appear at the input to the next stage due to the voltage drop in the output impedance.

From ohms law:-
It will in fact be (V * Input impedance of next stage) / (Input impedance of next stage + Output impedance of this stage).

Output current of stage 1 = Output V of stage 1 / (Input impedance of stage 2 + Output impedance of stage 1).

Due to series circuit Input current of stage 2 = Output current of stage 1.

Input voltage = Input current * input impedance


Thread Starter


Joined Aug 13, 2007
Thanks very much.

Anyone know how the overall input and output impedances are gained?

Basically I need to compress a large number of those elements to just one element with one input z, one output z, and one gain.